1. Technical Field
This application relates to computer storage devices, and more particularly to the field of handling remote computer storage device.
2. Description of Related Art
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may nor correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data stored therein.
In some instances, it may be desirable to copy data from one storage device to another. For example, if a host writes data to a first storage device, it may be desirable to copy that data to a second storage device provided in a different location so that if a disaster occurs that renders the first storage device inoperable, the host (or another host) may resume operation using the data of the second storage device. Such a capability is provided, for example, by the Remote Data Facility (RDF) product provided by EMC Corporation of Hopkinton, Mass. With RDF, a user may denote a first storage device as a master storage device and a second storage device as a slave storage device. Other incarnations of RDF may provide a peer to peer relationship between the local and remote storage devices. The host interacts directly with the local storage device, but any data changes made to the local storage device are automatically provided to a remote storage device using RDF. The local and remote storage devices may be connected by a data link, such as an ESCON link or a Fiber Channel link. The RDF functionality may be facilitated with an RDF adapter (RA), or a plurality of RA's, provided at each of the storage devices.
Implementation of RDF is facilitated using tables that indicate which tracks of data need to be modified at each location. For example, a local storage device having an RDF connection to a remote storage device may keep a table indicating which tracks have been written on the local storage device but not yet pushed (i.e., communicated via a data link) to the remote storage device. The table, called a “track table” contains an entry indicating the status of each track of the remote storage device. A track of the remote storage device is indicated as “invalid” after the data on the local storage device has been modified but before the modified data has been copied to the remote storage device. A track invalid condition may also occur when an RDF connection or configuration is initialized.
Tracks of a track table may be marked invalid by first reading a track into memory, or by at least reserving a slot for the track in the cache memory of the storage device. Once this has occurred, a process that modifies track table data entries of a track table may obtain a software lock for the track allowing exclusive access to the corresponding table data entry. The process may then modify the track table data entry corresponding to the track to mark the track as invalid. However, upon initialization of an RDF connection, it may be necessary to mark a significant number tracks as invalid. Reserving a cache slot for each of the tracks, locking each with a software lock, making the modification, and then releasing the lock could take a significant amount of time. In addition, reserving the necessary cache slots could cause other stored data not related to the initialization which is being used by other processes to be removed from cache, thus introducing additional inefficiencies. Accordingly, it would be useful to provide a mechanism for allowing setting invalid a large number of track table data entries without having to reserve a cache slot for each entry.